A systematic review of global epidemiological data on autism spectrum disorders (ASD) and pervasive developmental disorders (PDD) shows a median prevalence of 62/10,000. While prevalence estimates vary, there is no evidence of regional differences or strong impacts of ethnic/cultural or socioeconomic factors. However, data limitations in low-income countries restrict the ability to detect such effects. Prevalence has increased over time, likely due to broader diagnostic criteria, increased awareness, and improved service availability. The lack of data from many regions highlights the need for further research and capacity building in low- and middle-income countries. The review includes data from various regions, including Europe, the Western Pacific, Southeast Asia, the Eastern Mediterranean, and America. Prevalence estimates vary widely, with higher rates in some regions and lower in others. In Europe, the median prevalence for PDD is 61.9/10,000, while in the Western Pacific, it is 11.6/10,000. In Southeast Asia, the median prevalence is 100/10,000 in Sri Lanka and 29/10,000 in the United Arab Emirates. In America, the median prevalence for PDD is 65.5/10,000. In Africa, prevalence estimates are limited and preliminary. The review also highlights gender differences, with males consistently outnumbering females in most studies. Intellectual impairment is common among those affected, but the severity varies. The review concludes that while there is no evidence of regional differences in prevalence, there is a need for further research to better understand the global burden of PDD. The findings emphasize the importance of improving services and research in low- and middle-income countries.A systematic review of global epidemiological data on autism spectrum disorders (ASD) and pervasive developmental disorders (PDD) shows a median prevalence of 62/10,000. While prevalence estimates vary, there is no evidence of regional differences or strong impacts of ethnic/cultural or socioeconomic factors. However, data limitations in low-income countries restrict the ability to detect such effects. Prevalence has increased over time, likely due to broader diagnostic criteria, increased awareness, and improved service availability. The lack of data from many regions highlights the need for further research and capacity building in low- and middle-income countries. The review includes data from various regions, including Europe, the Western Pacific, Southeast Asia, the Eastern Mediterranean, and America. Prevalence estimates vary widely, with higher rates in some regions and lower in others. In Europe, the median prevalence for PDD is 61.9/10,000, while in the Western Pacific, it is 11.6/10,000. In Southeast Asia, the median prevalence is 100/10,000 in Sri Lanka and 29/10,000 in the United Arab Emirates. In America, the median prevalence for PDD is 65.5/10,000. In Africa, prevalence estimates are limited and preliminary. The review also highlights gender differences, with males consistently outnumbering females in most studies. Intellectual impairment is common among those affected, but the severity varies. The review concludes that while there is no evidence of regional differences in prevalence, there is a need for further research to better understand the global burden of PDD. The findings emphasize the importance of improving services and research in low- and middle-income countries.